Question

what can you use as a substitute for dumbbells?
a pen
a safety pin
a bottle of water

Explanation:

Dumbbells are used for weight - based exercises. A pen and a safety pin are too light and not suitable for providing the kind of weight resistance needed as a dumbbell substitute. A bottle of water, when filled, has a certain weight and can be held in a similar way to a dumbbell to provide resistance during exercises.

Answer:

C. A bottle of water (assuming the options are labeled A, B, C with C being "A bottle of water")